First-principles density-functional calculations were used to examine possible exchange mechanisms between an interstitial H atom and a deeply bound H at a Si-H bond. A low-energy pathway for exchange was determined which involved an intermediate metastable =SiH2 complex, with both H atoms strongly bound to the Si atom. The energy barrier to the exchange process was less than 0.2eV. This value was consistent with observations of H-D exchange in amorphous Si films.

Exchange of deeply trapped and interstitial hydrogen in silicon B.Tuttle, C.G.Van de Walle, J.B.Adams: Physical Review B, 1999, 59[8], 5493-7